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Have you had your molybdenum today?

Molybdenum, a little-known mineral found in beans, peas, and whole grains, keeps you alive. If it weren't for molybdenum, some of the chemicals in your body could build up to toxic levels.

But you're protected by a hardworking enzyme that relies on molybdenum. Called sulfite oxidase, the enzyme converts the unwanted chemicals to other compounds that your body can either use of get rid of.

Sulfite oxidase couldn't do this chemical chore without molybdenum. That's why the mineral warrants the status of "essential nutrient" --one that scientists have learned we can't live without.

For the most part, though, molybdenum's work as a nutrient remains a mystery. Better-known essential minerals such as calcium and iron, for instance, have a specific Recommended Dietary Allowance or RDA, like the ones you see on a box of cereal or a bottle of vitamin pills. Molybdenum has only a general range, notes ARS nutrition researcher Judith R. Turnlund.

Today's 75- to 250-microgram range of the gray-to-black mineral is "so slight it's barely visible," she says. She included amounts lower and higher than the range in a 4-month experiment at the ARS Western Human Nutrition Research Center in San Francisco. Eight healthy men aged 22 to 35 volunteered for the study.

During the experiment, they ate familiar foods like tuna salad or chicken casserole. Foods rich in molybdenum, however, were deliberately omitted from their menus.

To track molybdenum, the men were given special forms of the mineral, either as injections (three times during the study) or as an ingredient in a liquid formula served at meals. "In nature, molybdenum occurs as seven different atoms, or isotopes, each with its own atomic weight and each in an unchanging proportion to the other," explains Turnlund.

"By giving the volunteers purified doses of only two of these different molybdenum isotopes, we changed the natural ratios. That's how we traced the doses. Volunteers lived at the center for the entire study, so we could monitor everything they ate and drank. We think this is the most tightly controlled molybdenum study that's ever been done with humans."

Final results, expected later this year, may be used to set a new RDA. The experiment showcases two tests that could be streamlined for nutritionists and physicians of the future to use during vitamin-and-mineral checkups.

One option requires giving patients an extra load of any of several compounds that molybdenum-using enzymes will convert into other chemicals.

"When they were getting extra-low levels of molybdenum, says Turnlund, "we fed patients a high dose of one of these compounds. From this "loading test,' we could see that the molybdenum-using enzymes weren't getting enough of the mineral to keep up with the job of converting the compounds.

"Enzyme tests aren't new," she says, "but we're newly applying them to study molybdenum." UCLA scientist Marian E. Swendseid and former UCLA graduate student Glenn Chiang collaborated with Turnlund in this part of the experiment.

Another option relies on giving patients a dose of one of the forms of molybdenum that Turnlund used in her study. Later, a urine sample can be checked for the mineral.

The procedure Turnlund uses to hunt molybdenum--thermal ionization mass spectrometry--is too costly and cumbersome for most commercial medical labs. But newer generations of the technology should make it more affordable and easier to use, she says.

Until a test is ready and an exact RDA is set, though, how can people be sure they have all the molybdenum they need? "If you're eating three well-balanced meals a day," says Turnlund, "you're probably getting enough."

So what's the point of studying molybdenum? "If we tell people a mineral is essential," she says, "we should be able to tell them exactly how much they need. And we should have the data to back it up."
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Author:Wood, Marcia
Publication:Agricultural Research
Date:Apr 1, 1993
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